function Gravity(options) {
	this.gravityValue = (options && options.gravityValue) || 1;
	
	this.weightConstant = new WeightConstant;
	
	this.pull = function (graphicObject) {
		var currentY = graphicObject.getY();
		var delta = this._getMovementDistance(graphicObject);
		var movedY = currentY + delta;
		
		graphicObject.setY(movedY);
	};
	
	this._getMovementDistance = function (graphicObject) {
		var weight = graphicObject.getWeight(this.weightConstant);
		
		var result = Math.round(this.gravityValue * weight);
		
		return result;
	};
}